On Sat, Dec 15, 2018 at 1:23 PM Nathan Chancellor <natechancellor@xxxxxxxxx> wrote: > > While building arm32 allyesconfig, I ran into the following errors: > > arch/arm/lib/xor-neon.c:17:2: error: You should compile this file with > '-mfloat-abi=softfp -mfpu=neon' > > In file included from lib/raid6/neon1.c:27: > /home/nathan/cbl/prebuilt/lib/clang/8.0.0/include/arm_neon.h:28:2: > error: "NEON support not enabled" > > Building V=1 showed NEON_FLAGS getting passed along to Clang but > __ARM_NEON__ was not getting defined. Ultimately, it boils down to Clang > only defining __ARM_NEON__ when targeting armv7, rather than armv6k, > which is the '-march' value for allyesconfig. > > From lib/Basic/Targets/ARM.cpp in the Clang source: > > // This only gets set when Neon instructions are actually available, unlike > // the VFP define, hence the soft float and arch check. This is subtly > // different from gcc, we follow the intent which was that it should be set > // when Neon instructions are actually available. > if ((FPU & NeonFPU) && !SoftFloat && ArchVersion >= 7) { > Builder.defineMacro("__ARM_NEON", "1"); > Builder.defineMacro("__ARM_NEON__"); > // current AArch32 NEON implementations do not support double-precision > // floating-point even when it is present in VFP. > Builder.defineMacro("__ARM_NEON_FP", > "0x" + Twine::utohexstr(HW_FP & ~HW_FP_DP)); > } > > Ard Biesheuvel recommended explicitly adding '-march=armv7-a' at the > beginning of the NEON_FLAGS definitions so that __ARM_NEON__ always gets > definined by Clang. This doesn't functionally change anything because > that code will only run where NEON is supported, which is implicitly > armv7. > > Link: https://github.com/ClangBuiltLinux/linux/issues/287 > Suggested-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Nathan, Thanks for sending the patch, and thanks to Ard for the suggestion. Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > Documentation/arm/kernel_mode_neon.txt | 4 ++-- > arch/arm/lib/Makefile | 2 +- > arch/arm/lib/xor-neon.c | 2 +- > lib/raid6/Makefile | 2 +- > 4 files changed, 5 insertions(+), 5 deletions(-) > > diff --git a/Documentation/arm/kernel_mode_neon.txt b/Documentation/arm/kernel_mode_neon.txt > index 525452726d31..b9e060c5b61e 100644 > --- a/Documentation/arm/kernel_mode_neon.txt > +++ b/Documentation/arm/kernel_mode_neon.txt > @@ -6,7 +6,7 @@ TL;DR summary > * Use only NEON instructions, or VFP instructions that don't rely on support > code > * Isolate your NEON code in a separate compilation unit, and compile it with > - '-mfpu=neon -mfloat-abi=softfp' > + '-march=armv7-a -mfpu=neon -mfloat-abi=softfp' > * Put kernel_neon_begin() and kernel_neon_end() calls around the calls into your > NEON code > * Don't sleep in your NEON code, and be aware that it will be executed with > @@ -87,7 +87,7 @@ instructions appearing in unexpected places if no special care is taken. > Therefore, the recommended and only supported way of using NEON/VFP in the > kernel is by adhering to the following rules: > * isolate the NEON code in a separate compilation unit and compile it with > - '-mfpu=neon -mfloat-abi=softfp'; > + '-march=armv7-a -mfpu=neon -mfloat-abi=softfp'; > * issue the calls to kernel_neon_begin(), kernel_neon_end() as well as the calls > into the unit containing the NEON code from a compilation unit which is *not* > built with the GCC flag '-mfpu=neon' set. > diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile > index ad25fd1872c7..0bff0176db2c 100644 > --- a/arch/arm/lib/Makefile > +++ b/arch/arm/lib/Makefile > @@ -39,7 +39,7 @@ $(obj)/csumpartialcopy.o: $(obj)/csumpartialcopygeneric.S > $(obj)/csumpartialcopyuser.o: $(obj)/csumpartialcopygeneric.S > > ifeq ($(CONFIG_KERNEL_MODE_NEON),y) > - NEON_FLAGS := -mfloat-abi=softfp -mfpu=neon > + NEON_FLAGS := -march=armv7-a -mfloat-abi=softfp -mfpu=neon > CFLAGS_xor-neon.o += $(NEON_FLAGS) > obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o > endif > diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c > index a6741a895189..4600b62d845f 100644 > --- a/arch/arm/lib/xor-neon.c > +++ b/arch/arm/lib/xor-neon.c > @@ -14,7 +14,7 @@ > MODULE_LICENSE("GPL"); > > #ifndef __ARM_NEON__ > -#error You should compile this file with '-mfloat-abi=softfp -mfpu=neon' > +#error You should compile this file with '-march=armv7-a -mfloat-abi=softfp -mfpu=neon' > #endif > > /* > diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile > index 2f8b61dfd9b0..bfec7c87c61e 100644 > --- a/lib/raid6/Makefile > +++ b/lib/raid6/Makefile > @@ -25,7 +25,7 @@ endif > ifeq ($(CONFIG_KERNEL_MODE_NEON),y) > NEON_FLAGS := -ffreestanding > ifeq ($(ARCH),arm) > -NEON_FLAGS += -mfloat-abi=softfp -mfpu=neon > +NEON_FLAGS += -march=armv7-a -mfloat-abi=softfp -mfpu=neon > endif > CFLAGS_recov_neon_inner.o += $(NEON_FLAGS) > ifeq ($(ARCH),arm64) > -- > 2.20.1 > -- Thanks, ~Nick Desaulniers